Current flexible display architectures, such as those used for flexible organic light emitting diodes (FOLEDs), require a transparent barrier layer that prevents oxygen gas ingress into the device's active components. These devices require an oxygen transmission rate (OTR) below 10−5 cc/(m2·day·atm) to achieve sufficient performance requirements (i.e., tens of thousands of hours of operation) in ambient environments. Similar layers with very low permeation rates to atmospheric gases are also key components for a variety of packaging applications, including food and pharmaceuticals. Commonly used metallized plastics have sufficiently low permeation rates for most applications, but lose their utility when product visibility is desired, as in food packaging, or even a requirement, in the case of FOLEDs. A heavily investigated alternative to the metallization of plastics is the deposition of thin metal-oxide layers via vacuum-based processes, such as physical vapor deposition or plasma-enhanced chemical vapor deposition. These inorganic barrier layers exhibit very low OTR at thicknesses as low as 100 nm. Despite exhibiting impressive barrier, low adhesion strength to plastics and inherent brittleness, because they are continuous ceramic sheets, makes these films prone to cracking and loss of barrier performance. Layering these ceramic nanocoatings with UV-curable polymer has been shown to reduce permeability, but these multilayered coatings require very complex fabrication techniques that significantly increase cost.
Clay-filled polymer composites, where individual or stacks of clay platelets are randomly dispersed in bulk polymer, offer an alternative to deposited layers on a plastic substrate. Clay nanoplatelets can be thought of as impermeable barrier particles that extend a penetrating gas molecule's travel due to their creation of a highly tortuous path. The tortuous pathway concept is the key to polymer/clay composites' gas barrier performance. In contrast to fully inorganic coatings, polymer/clay nanocomposites generally maintain desirable mechanical properties. Unfortunately, these composites typically suffer from clay aggregation and random platelet alignment, yielding poor transparency and relatively high gas permeation rates. Recent one-pot mixtures of clay in polymer have led to significant improvements in platelet alignment, but they still exhibit haziness, relatively high OTR values, and are orders of magnitude thicker than ceramic nanocoatings.
A recent review of the clay-based nanocomposites landscape stated the key to success for polymer/clay nanocomposites is the ability to incorporate uniformly dispersed, highly exfoliated, individual clay platelets in a polymer matrix. The vast literature on this topic further suggests that finding a balance between flexibility, transparency, and barrier is vital to the successful encapsulation of flexible electronic devices.
Despite the advances noted above, there exists a need to for a transparent barrier film that is effective against humidity and oxygen penetration. The present invention seeks to fulfill this need and provides further related advantages.